W) CURVE A 



/3-**YS OF OKA 

 ALU Wh/nJ 



Phil. Mag. Ser, 6, Tol. 19, PL XII. 



Fig. 13. 

 2 4 6 8 10 12 



y-R/iYS OF RAQIUM 

 LEAD 

 BR/ISS ELECTROSCOPE 



A ALONE 



B WW LEAD SCREENS 



OS CM. THICK. 



